This invention relates to a document scanning system for use with a copier or a duplicator. More particularly, the invention relates to a document scanning system for scanning original documents which may be in the form of either individual sheets or bound volumes and generating corresponding scanning signals suitable for loading into a memory. Once loaded into memory, the scanned information may be used for controlling the operation of a dot matrix printing device, such as an ink jet printer. Typical ink jet printers which might be used for such a purpose are disclosed in Frey U.S. Pat. No. 4,010,477, Paranjpe U.S. Pat. No. 4,085,409, and in Vedder U.S. Pat. No. 4,234,884.
Typical prior art scanners for use in ink jet copying are shown in Nodov U.S. Pat. No. 4,258,395 and in Gamblin et al U.S. Pat. No. 4,155,103. In both of these prior art references, the scanning is carried out by a rotating mirror while the original documents are held stationary on a transparent platen. Nodov's scanner is connected for direct control of the printer, while Gamblin et al utilizes a memory for temporary storage of the scanned information. Other prior art scanners are shown in Gunning U.S. Pat. No. 4,205,350 and in U.K. patent specification 1,531,401, both of which show the use of lasers for scanning original documents to produce scanning signals which are read into a memory. After the documents have been scanned, the stored image information is read out from memory and used to modulate the scanning laser for production of latent electrostatic images on a photoconductive surface.
All scanning systems disclosed in the above-mentioned references comprise movable optical elements which scan documents which are manually positioned on a platen. Other prior art scanning systems include automatic sheet feeding devices which carry original sheet-type documents across the viewing platen. Such systems are capable of performing manually initiated scanning of bulky documents as well as higher speed scanning of individual sheets. Typical systems of this type are disclosed in Phillips et al U.S. Pat. No. 4,043,550 and in Caldwell U.S. Pat. No. 4,043,665, both of which are used in electrostatic copiers.
Other types of prior art scanning systems known in the electrostatic copying field have a sheet scanning station which is separate from the platen utilized for copying bulky documents. Examples of scanners of this type are disclosed in Suzuki et al U.S. Pat. No. 4,158,497, Yanagawa et al U.S. Pat. No. 4,178,093 and in Knechtel U.S. Pat. No. 4,110,030. The Knechtel reference also discloses front and back side scanning of sheet-type original documents. Finally, reference is made to Kelly U.S. Pat. No. 3,844,653 which discloses front and reverse side scanning of sheet-type original documents at separate scanning stations.
Electrostatic copiers are severly constrained by the requirement of projecting an image of the original document upon a photoconductive surface once for each copy produced, and the scanners which are employed for such purposes are not entirely suitable for ink jet copying. Those scanners which have been utilized for ink jet copiers have not had automatic sheet feeding capability. Thus the prior art ink jet copiers have had extremely limited versatility and have not been able to perform many of the tasks required of a practical high speed duplicator. There has therefore been a need for an improved scanning system which is suitable for use with an ink jet copier or duplicator and which can scan a manually positioned bulky document and also feed and scan both sides of sheet-type documents.